Concrete Architecture to Service More Than 4 Million Catholics

The Cathedral of Our Lady of the Angels is the third largest cathedral (195,000 square feet) in the world and the first Catholic cathedral built in the Western United States in over 30 years. Representing the largest use of exposed architectural concrete in California, this landmark cathedral is the first seismically base isolated major new religious structure. It is also flanked by a freestanding 160-foot tall campanile (bell tower), that is also base isolated. Suited for 6,000 people, the adjacent 2.5-acre grand public plaza is used for liturgical, cultural, and civic events. It is dotted with artwork and also provides a conference center, clerical residence and three-level subterranean parking garage for 600 cars.

Soaring to a height equivalent to 150 feet, the $144.3 million cathedral has seating for 3,000 people. It offers a 58,000-square-foot nave, giving visitors an unparalleled spiritual experience. Light floods through the window silhouette of a large concrete cross above the altar. The stunning space is illuminated by windows composed of 24,000 feet of thinly veined Spanish alabaster. Stairs lead to the basement housing the St. Vibiana's Chapel and the mausoleum, one of the largest cathedral burial vaults in the world.

The entire construction site for the cathedral sits atop the Elysian Park Fault, expected to produce severe ground motion (up to a 7.0 magnitude) in the event of an earthquake. To counter this threat, the project team utilized and implemented advanced strategies with concrete shear walls to achieve a 500-year service life for the structure and building systems. The resulting building sits on base isolators (149 replaceable rubber bearings and 47 flat slide bearings) which means the entire building can move about 27 inches in each direction during earthquakes.

The campanile structural system consists of cast-in-place concrete slabs and beams spanning between colored architectural concrete walls. Friction pendulum bearings were used to support the campanile at four bearing points, each in the middle of an 80-inch diameter stainless steel saucer.

Lightly colored, sandblasted architectural concrete was selected for the 450,000-square-foot exterior and interior wall surfaces of the cathedral itself and for the additional 200,000 square feet of walls in the surrounding buildings. To complete the project, 59,580 cubic yards of concrete was cast, of which 52 percent represented adobe color with precise shingle pattern. The walls varied in thickness from 1- to 5- feet and pitched at angles ranging from vertical to 30 degrees from the horizontal, with no two walls intersecting at 90 degrees. This complex configuration resulted in 850 different corner conditions.

As a symbol of timelessness, the cathedral construction aimed for extraordinary material durability beyond the robust walls and seismic isolators in one of the smoggiest urban cores of the nation. To ensure longevity, measures included a restriction of the water-cementitious materials ratio to maximum of 0.45, a light-colored pozzolanic admixture to protect the concrete from chemical attacks, and an additional 1 inch of concrete cover for the reinforcing bars. In addition to the synthetic fibers and high-silane content sealers, stainless steel was specified for the reinforcement at the horizontal surfaces, for the tie wires, and for the waterstops at predetermined construction joints.

The procedures used for concrete mix design, forming, placing and curing were developed during a year of research with help from UC Berkeley. Extensive mock up testing with special attention to thermal stresses and formwork removal was used to mediate unforeseen conditions. As a result of an outstanding collaborative effort of the construction/design/research team, the cathedral opened in 2002 with exceptional quality. It will serve as a sacred edifice as well as an emergency shelter for centuries to come.